Previous attempts to eliminate tack and cold flow from polymers have included the use of various filler materials such as silica, carbon black, mica, and a variety of fibers. While such treatment can provide sufficient integrity to cold flow materials for them to hold a shape, it does little to eliminate surface tack. Moreover, high filler loadings can extend to several times the weight of the polymer thereby restricting the usage of the polymer to applications where the filler can be tolerated.
In order to provide tack-free surfaces, surface treatment of polymers is also possible. U.S. Pat. No. 4,029,862 is directed toward a process of chlorinating solid linear polyethylene in order to impart improved handling characteristics such as non-agglomeration. The process is not directly applicable to sticky, cold-flowable polymers, however, inasmuch as the polymer particles treated according to the patent had a free-flowing nature, suitable for extrusion operations, prior to the treatment.
U.S. Pat. No. 4,431,765, owned by the Assignee of record, discloses a process for forming free flowing particles of polybutadiene thermoset resins by adding certain filler materials in an amount sufficient to render the resin free flowing and resistant to cold flow. The process calls for the two components to be mixed together to form a blend which is thereafter chopped into small particles.
Russian Pat. No. 729,066 teaches the preparation of free-flowing rubber crumb from latex by treatment of the latex with a hypochlorite solution.
Finally, U.S. Pat. No. 3,853,796, also owned by the Assignee of record, discloses high stress-low elongation polymer compositions comprising a copolymer of nylon and a conjugated diene, blended with reinforcing fibers and optionally with a rubber polymer. The patent does not address cold flow or tack free compositions and differs from the present invention in that the rubber added is added after the copolymer has been formed.
Thus, the art disclosed herein has not provided a process for eliminating both undesirable surface tack and cold flow from polymers and copolymers that exhibit these properties.